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Paris, July 2, 2008

To multiply, ant colonies adapt to environmental conditions

By combining field work in Australia with mathematical modeling, three scientists from the laboratoire Fonctionnement et évolution des systèmes écologiques (CNRS/Université Pierre et Marie Curie/ENS Paris) have shown that the quality and quantity of winged queens produced by colonies of the Rhytidoponera ant vary according to environmental conditions. In certain cases, colonies even stop producing founding queens and spread solely by splitting up the colony. This work is published in the July 2008 issue of the journal The American Naturalist.

Ants have colonized every habitat on land in part because they have a number of strategies for establishing new colonies. Queens can found new colonies independently: after aerial dispersion, each queen produces her first workers alone. Alternatively, queens can leave their original colony accompanied by a group of workers. Known as “colony fission,” this method increases survival rates for queens because they are never alone.However, because worker ants do not have wings, long distance dispersion is not possible.

The quality and quantity of winged queens produced by ants of the genus Rhytidoponera vary with environmental conditions, according to scientists from the laboratoire Fonctionnement et évolution des systèmes écologiques (CNRS/Université Pierre et Marie Curie/ENS Paris). They studied Rhytidoponera impressa, a group of carnivorous ants that hunts small insects and is found along the entire east coast of Australia. The scientists collected ant colonies before nuptial flights and measured the metabolic reserves of the young queens. They found that colonies in tropical forests (in northern Australia) produce numerous, low quality queens (i.e. with poor metabolic reserves). In contrast, in southern temperate forests where harsher winters make the availability of prey less reliable, colonies produce fewer but heavier queens. These queens, with greater fat reserves, do not have to forage as much and thus have better survival rates.

In addition, the scientists found that if independent foundation of new colonies becomes ineffective, colonies multiply by splitting up the group. In this case, they do not produce more queens: since worker ants in this group can mate, they provide a less costly means of laying eggs than queens.

Mathematical modeling indicated that these changes in the colony’s reproductive strategy were caused by environmental parameters such as the quantity of food and environmental fluctuations. However, the scientists also found that there are more queens in nature than the model predicts (given that they can be “replaced” by worker ants), and this is probably due to the fact that queens add an important element to colonization in that they can disperse aerially.